The usefulness of a battery-powered device such as a portable personal computer will typically increase if the time duration of its battery sustained operation can be prolonged. Given the fixed amount of electricity which a battery can store, the time duration of a battery-powered device must in turn be prolonged by conservation of its power consumption.
Power consumption is conserved in prior art by switching a device's circuits to a low-power, standby mode at times when operation of the circuits is not needed. Such conservation is commonly applied to keyboard devices where the "think" time of its operators is usually comparable, if not longer, than the "keying-in" time.
One prior art method of power conservation is disclosed in U.S. Pat. No. 4,649,373, "Powered Conservation System in Battery Powered Keyboard Device Including A Microprocessor" issued to P.M. Bland et al. Another prior art power conservation method is disclosed in Application Notes AP-252 of the "Microcontroller Handbook" published by Intel Corporation, page 9-54. In these prior art methods, one or more output port of the microprocessor is used to set the device into a lower power, standby mode.
In accordance with the present invention, power conservation is achieved without the use of any input/output port of the microprocessor.